A cellulose derivative film is applied to an optical film such as a polarizing plate protective film, an optical retardation film, or an optical compensation film, since it has excellent optical properties.
It is essential that an additive such as a plasticizer or a UV absorbent be added to the cellulose derivative film in order to improve its processability or moisture vapor transmittance. However, the addition has a problem which causes bleeding-out or volatilization of the additive, resulting in lowering of dimensional stability and storage stability of the film.
A polarizing plate is generally one in which a polarizing plate protective film comprised of triacetyl cellulose is provided on both surfaces of a polarizing film comprised of a uniaxially stretched dichroic dye dyed polyvinyl alcohol, in order to shield light or moisture. A crystal liquid display comprising such a polarizing plate is often used outdoors as in a car navigation system or a cell phone, and its durability under various circumstances is required. However, the polarizing plate protective film in a conventional polarizing plate varies with time, and has a problem in that the edge of the polarizing plate transmits light, resulting in phenomenon of edge whitening.
Improvement of dimensional stability is required in another optical film employing a cellulose derivative film. For example, dimensional stability of an optical retardation film is required in view of stability of its optical properties. Recently, as a high resolution image and a color image reproduction are required in a display of a note board type personal computer or a cell phone, an optical film with high performance having an anti-reflection property or an anti-static property has been sought. Such an optical film has been developed which comprises a cellulose derivative substrate with high transmittance and a functional layer such as a metal oxide layer directly or through another layer on the substrate. However, this optical film has still a problem in that its optical properties lower due to dimensional change of the substrate.
The optical film in the invention is a functional film used in various displays such as a liquid crystal display, a plasma display, an organic EL display, a field emission display, and an electronic paper display. Examples of the optical film include a polarizing plate protective film, an optical retardation film, a reflection plate, a viewing angle increasing film, an optical compensation film, an antiglare film, an antireflection film, an illuminance increasing film, a color correction filter, a color separation film, a UV or IR absorbing film, an antistatic film, and an electrically conductive film.